1. Field of the Invention
The present invention relates to a clothing drying machine and a method for sensing a dryness level using the same, and more particularly, to a clothing drying machine, which performs drying operation in various dryness levels and a method for sensing a dryness level using the clothing drying machine.
2. Description of the Related Art
Generally, a clothing drying machine includes a housing forming an external structure, a drum installed in the housing for containing laundry to be dried, a heating duct for generating hot air to be supplied to the drum, a hot air inlet channel for guiding the hot air generated form the heating duct to the drum, and a hot air outlet channel for guiding the hot air discharged from the drum to the outside.
The drum is rotatably installed in the housing, and an air blast fan for generating force for flowing the hot air is installed in the hot air outlet channel. The hot air circulates into the drum and the duct by the operation of a driving motor for simultaneously driving the drum and the air blast fan, thereby drying the laundry.
A conventional clothing drying machine, which is disclosed by Korean Laid-open Publication No. 2002-62446, senses a dryness level of clothing using an electrode sensor and a thermistor. The electrode sensor determines the dryness level of the clothing according to a sensed voltage using a principle, in which the voltage is increased when laundry having a high humidity contacts a metal plate, and the thermistor allows control of the drying of the clothing using a principle in which electric resistance varies according to a variation of temperature. That is, the thermistor determines a dryness level of the clothing by sensing the temperature of air discharged from the drum to the outside. As shown in FIGS. 1 and 2, when a driving motor and a heater are driven after clothing to be dried is supplied to the inside of a drum of the drying machine, and a drying operation starts, the thermistor senses a temperature (T) of discharged air after the clothing is dried, and the electrode sensor senses a dried state value (V) of the clothing in the drum.
When the drying of the clothing is in progress (S10), the dried state value (V) of the clothing and the temperature (T) of the air vary based on the curves of V and T versus time (t) shown in FIG. 2. A control unit periodically senses the dried state value (V) of the clothing (S30) and the temperature (T) of the air (S20), and determines whether or not the temperature (T) of the air reaches a predetermined upper limit (T1) (S40). When it is determined that the temperature (T) of the air reaches the predetermined upper limit (T1), the control unit stops the operation of the heater (S50), and when it is determined that the temperature (T) of the air is less than a predetermined lower limit (T2) (S60), the control unit turns on the heater (S70). The above procedure is repeated until it is sensed that the dried state value (V) of the clothing is more than 5V (S80). When the dried state value (V) of the clothing is more than 5V, it is determined that the drying of the clothing is completed and the drying operation is terminated (S90).
In the above-described conventional method for sensing a dryness level of clothing, when the temperature (T) of the air reaches the predetermined upper limit (T1) and the thermistor starts its control operation, the clothing has been comparatively highly dried. Accordingly, the above conventional method cannot cope with the situation in which a user wants a low dryness level of the clothing so that the clothing has a high remaining moisture content.
Further, if a dryness level of the clothing is determined using a voltage value inputted to the electrode sensor, the voltage value momentarily may fluctuate widely. Accordingly, in this case, it is difficult to sense a precise dryness level of the clothing.